1. Field of the Invention
The present invention relates to a small watercraft, and more particularly to a personal watercraft that gains a propulsion force by driving a water jet pump.
2. Description of the Related Art
In recent years, jet-propulsion personal watercraft, which are one type of small watercraft, have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft comprises an engine mounted in a space within the watercraft which is surrounded by a hull and a deck. Conventionally, a two-cycle engine has been typically employed in the personal watercraft.
The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom hull surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled. In the jet-propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to right or to the left.
In the engine mounted in the personal watercraft, oil is used to lubricate various components such as bearings to allow these components to operate smoothly, cool these components, or the like. In the two-cycle engine, the engine components are lubricated by the oil mixed in a fuel and suctioned into a crankcase together with the fuel.
In certain personal watercraft, four-cycle engines have been recently mounted instead of the two-cycle engines. The four-cycle engines employ a wet-sump system or a dry-sump system to control the oil in the engine. The oil is delivered at a proper pressure by an oil pump and circulates within the engine independently of the fuel.
In order for the oil to fully function in the four-cycle engine, the oil delivered by the oil pump is required to have a pressure (hydraulic pressure or oil pressure) in a proper range. However, in some cases, the oil is diluted by the fuel mixed therein due to a blow-by gas or the like, and thereby the hydraulic pressure is reduced and becomes lower than the proper range. Also, since the oil is consumed by long-time drive of the engine, the hydraulic pressure is reduced.
Such a reduced hydraulic pressure is undesirable to the engine. Especially in the four-cycle engine, the reduced hydraulic pressure causes insufficient lubrication, and it is therefore necessary to notify a rider of such reduction. In the conventional method, the rider is notified of reduction of the hydraulic pressure by lighting an oil lamp provided on an instrument panel upon detection of the reduction.
In general, a rotational shaft of the oil pump is coupled to a crankshaft of the engine. The hydraulic pressure increases with increasing engine speed, and is low during low engine speed, for example, at idling speed. Accordingly, in the conventional method, the oil lamp is configured not to be lighted when the hydraulic pressure is reduced due to the low engine speed, and to be lighted only when the hydraulic pressure becomes a value lower than a predetermined value (e.g., about 0.1 kg/cm2 ) due to, for example, consumption of the oil. In this setting, it is necessary to set a threshold of the hydraulic pressure at which the oil lamp are lighted to a relatively low value. Under this condition, if the hydraulic pressure is slightly reduced from a proper value due to dilution of the oil or the like, this cannot be detected.
In another possible method, the rider is notified of slight reduction of the hydraulic pressure due to dilution of the oil or the like, by using a hydraulic-pressure indicator provided to sequentially display a hydraulic-pressure value. This leads to a very high cost.
The above described conditions may also occur in small watercraft other than the personal watercraft.